[rules-dev] salience alternative with before/after

[Mark Proctor]

Davide has suggested a good idea.

Now that rules support annotations, and annotations with values. We 
should add a before/after keyword to each rule. before/after would then 
take a list of annotations. The idea is to use this to generate salience 
under the covers.

rule resetBalance before( @cashflow ) when then end

rule debit @cashflow when then end

rule credit @cashflow when  then end

rule printBalance after(@cashflow ) when then end.

Salience gives one rule priority over another, thus it's declaring an 
implicit relationship between rules. Yet it's a magic number that 
doesn't easily show this relation, and as the rulebase grows it can be 
very hard to determine those relationships as specified by salience from 
reading the rules. before/after allows you to specify declarative the 
relationships betwen rules in a more maintainable and readable way, even 
if under the covers it's just generating:

rule resetBalance salience 100 when then end

rule debit salience 0  when then end

rule credit salience 0 when  then end

rule printBalance saliance -100 when then end.

Yes there are agenda-groups and ruleflow-groups, but they can be a bit 
cumbersome compared to the simplicity of using salience. This way we get 
the simplicity of using salience, without the downfalls of it being a 
magic number.

What do people think? Any ideas on how we can improve this? At build 
time it would have to report impossible to resolve relationships and barf.

Mark